1. Field of the Invention
The present invention relates to a magnetic recording medium and a method for manufacturing the same. More particularly, the present invention relates to a magnetic recording medium used in magnetic recording devices, for example in computers.
2. Description of the Related Art
High quality magnetic recording mediums require both high recording density and low noise. In an effort to achieve these goals, various compositions and structures for magnetic layers and non-magnetic under-layers have been proposed. Recently, a magnetic layer called a granular magnetic layer has been proposed having a structure, in which a ferromagnetic grain is surrounded by a non-magnetic and non-metallic substance, such as an oxide or a nitride.
Technology related to the granular magnetic layer is shown in Japanese Unexamined Patent Application Publication No. H8-255342 and U.S. Pat. No. 5,679,473.
In Japanese No. H8-255342, a method for manufacturing a magnetic recording medium comprises multiple steps. These steps include, sequentially depositing, on a non-magnetic substrate, a non-magnetic film, a ferromagnetic film and a non-magnetic film, and heat-treating the resulting lamination. This process forms a recording layer in which ferromagnetic grains are dispersed in the non-magnetic film.
The technology of this disclosure proposes to attain low noise by means of forming a granular recording layer in which ferromagnetic grains are dispersed in a non-magnetic film structure. Silicon oxide and nitride are used for the non-magnetic film in this technology.
U.S. Pat. No. 5,679,473 discloses the formation of a low noise granular recording film by means of RF sputtering using a CoNiPt target containing an oxide additive, such as SiO2. In this granular recording film, each magnetic grain is surrounded and separated from others by a non-magnetic oxide.
Reduced recording noise is obtained since each of the magnetic grains in the above granular magnetic film is physically separated along a grain boundary by a non-magnetic and non-metallic phase thus reducing magnetic interaction between the magnetic grains, and suppressing the formation of magnetic domain walls having a zigzag shape at the transition region of a recording bit.
In conventional Coxe2x80x94Cr metallic magnetic film, to reduce magnetic interaction between the individual magnetic grains, chromium is segregated from a cobalt alloy magnetic grain toward a grain boundary. In the conventional Coxe2x80x94Cr metallic magnetic layer, when laminating the layer, heating the substrate to 200xc2x0 C. is essential for sufficient segregation of chromium.
In the conventional granular magnetic layer, the grain boundary phase is a non-magnetic and a non-metallic substance, which segregates more easily than the conventional, thereby enhancing isolation of the magnetic grains.
The granular magnetic layer has the advantage that the non-magnetic and non-metallic substance segregates evenly in lamination without heating.
Unfortunately, high density, together with low noise of magnetic recording mediums require both reduction of magnetic interaction between the grains due to enhancement of the segregation structure in the magnetic layer, and control of crystal orientation of Coxe2x80x94Cr ferromagnetic grain.
More specifically, the c-axis of the ferromagnetic grains requires a hexagonal closed-packed grain structure to align the grains in the plane of the film surface. The control of the crystal orientation of the magnetic layer in conventional magnetic recording mediums having metallic magnetic layers is accomplished by controlling structure and crystal orientation of the non-magnetic under-layer.
In conventional magnetic recording mediums having a granular magnetic film, the effect of an under-layer is small since the ferromagnetic grains are separated from the under-layer by the segregation substance comprising the grain boundary, namely an oxide.
A publication entitled xe2x80x9cEffect of Crxe2x80x94Mo under-layer in CoPtxe2x80x94SiO2xe2x80x9d in xe2x80x9cNihon Oyojiki Gakkaishixe2x80x9d ((Journal of the Japanese Society for Applied Magnetics) Vol. 23, No. 4-2, pp. 1017-1020 (1999)) discloses that using an under-layer of a special composition of a Cr-Mo alloy (having a preferential orientation in the (110) plane) causes preferential orientation of the (100) plane and the (101) plane in ferromagnetic grains in a granular magnetic layer. Use of such an under-layer results in an improvement of magnetic property and electromagnetic conversion characteristics.
Unfortunately, when a ferromagnetic grain has a preferential orientation of it""s the (101) plane, the c-axis does not align parallel to the film surface. Instead, the c-axis rises up from the film surface at an angle. As a result, the magnetic anisotropy of the crystal grain contains a component perpendicular to the film surface. This perpendicular component creates a corresponding perpendicular component of magnetization, resulting in increased media noise.
The preferential orientation of the (101) plane in the ferromagnetic grain is caused by the preferential orientation of (110) plane in the CrMo alloy under-layer. As a result, the orientation control of a magnetic layer, disclosed in the reference, must be regarded as insufficient. In sum, more precise control of crystal orientation is needed for obtaining a low noise medium.
It is an object of the present invention to provide a magnetic recording medium that overcomes the concerns raised above.
It is another object of the present invention to provide a magnetic recording medium and method for manufacture that allows more precise control of crystal orientation without thermal processing.
It is another object of the present invention to provide a magnetic recording medium having a low recording noise.
It is another object of the present invention to provide a method for manufacturing a magnetic recording medium that has low noise.
It is another object of the present invention to provide a medium and manufacturing method therefore which achieves the above objects and overcomes the above-noted concerns.
Briefly stated, the present invention provides a magnetic recording medium achieves excellent noise reduction by controlling the crystal orientation of a magnetic layer without thermal processing. The magnetic recording medium includes multiple layers laminated to a substrate. These layers include at least the magnetic layer and a non-magnetic under layer. The magnetic layer has a granular structure consisting of ferromagnetic grains with a hexagonal close-packed structure and non-magnetic grain boundaries composed mainly oxide or a nitride. The non-magnetic under-layer is a material having a body centered cubic crystal structure with a preferential orientation along a (200) plane parallel to a film surface of the under-layer. The present invention also provides a manufacturing process for the above-noted product.
According to an embodiment of the invention there is provided a magnetic recording medium, comprising: a non-magnetic substrate, at least a non-magnetic under-layer on the non-magnetic substrate, at least a magnetic layer on the non-magnetic under-layer, at least a protective layer on the magnetic layer, the magnetic layer having a substantially granular structure, the substantially granular structure including at least a plurality of ferromagnetic grains having a non-magnetic grain boundary phase surrounding the plurality of ferromagnetic grain, the plurality of ferromagnetic grains each having a hexagonal close-packed lattice structure, the non-magnetic grain boundary phase including at least one of a metal oxide and a metal nitride, and the non-magnetic under-layer having a body-centered cubic crystal lattice structure and a preferential crystal orientation of (200) plane parallel to a film surface of the non-magnetic under-layer, whereby a c-axis of each the ferromagnetic grain preferentially aligns parallel to the film surface and minimizes a perpendicular component of magnetization in the magnetic layer thus reducing noise.
According to another embodiment of the invention there is provided a magnetic recording medium, further comprising: a non-magnetic intermediate layer between the magnetic layer and the non-magnetic under layer, and the non-magnetic intermediate layer having a hexagonal close-packed lattice structure.
According to another embodiment of the invention there is provided a magnetic recording medium, further comprising: a non-magnetic alignment-control layer, the non-magnetic alignment-control layer between the non-magnetic under layer and the non-magnetic substrate, the non-magnetic alignment control layer having a cubic lattice structure, and the non-magnetic alignment-control layer having a crystal orientation plane parallel to a second film surface of the non-magnetic alignment-control layer, and the crystal orientation plane is a (100) plane.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the non-magnetic alignment-control layer includes at least one material selected from a group consisting of oxides of Mg, Ti, and V, and carbides and nitrides of Ti, Zr, Hf, NB, Ta, Mo, and W.
According to another embodiment of the invention there is provided a magnetic recording medium, further comprising: a non-magnetic intermediate layer, the non-magnetic intermediate layer between the magnetic layer and the non-magnetic under layer, the non-magnetic intermediate layer having a hexagonal close-packed lattice structure, anon-magnetic alignment-control layer, the non-magnetic alignment control layer between the non-magnetic under layer and the non-magnetic substrate, the non-magnetic alignment-control layer having a cubic lattice structure, and the non-magnetic alignment-control layer having a crystal orientation plane parallel to a second film surface of the non-magnetic alignment-control layer, and the crystal orientation plane is a (100) plane.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the non-magnetic alignment-control layer includes at least one material selected from a group consisting of oxides of Mg, Ti, and V, and carbides and nitrides of Ti, Zr, Hf, NB, Ta, Mo, and W.
According to another embodiment of the invention there is provided a magnetic recording medium, further comprising: a seed layer, the seed layer between at least the non-magnetic alignment-control layer and the substrate, and the seed layer having an amorphous structure.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the seed layer includes of a nickel layer containing from 10 at % to 40 at % of phosphorus.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the seed layer includes a silicon layer containing from 25 at % to 55 at % of oxygen.
According to another embodiment of the invention there is provided a magnetic recording medium, further comprising: a seed layer, the seed layer between at least the non-magnetic alignment-control layer and the substrate, and the seed layer having an amorphous structure.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the seed layer includes of a nickel layer containing from 10 at % to 40 at % of phosphorus.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein the seed layer includes a silicon layer containing from 25 at % to 55 at % of oxygen.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the non-magnetic substrate includes a material selected from the group consisting of crystallized glass, chemically strengthened glass and resin.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the non-magnetic under layer has a thickness from 5 nm to 100 nm.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the non-magnetic intermediate layer has a thickness from 2 nm to 20 nm.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the non-magnetic intermediate layer has a thickness from 2 nm to 20 nm.
According to another embodiment of the invention there is provided a magnetic recording medium, wherein: the plurality of ferromagnetic grains are crystalline grains of a CoPt alloy, and the CoPt alloy is doped with at least one material selected from a group consisting of Cr, Ni, and Ta, whereby magnetic recording properties are improved.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium comprising the steps of: selecting a non-magnetic substrate, laminating at least a non-magnetic under-layer on the non-magnetic substrate, the non-magnetic under-layer being a material having a body-centered cubic lattice structure and preferential crystal orientation plane in a (200) plane parallel to a film surface of the non-magnetic under-layer, laminating at least a magnetic layer on the non-magnetic under-layer, the magnetic layer including a plurality of ferromagnetic grains having a hexagonal close-packed structure and a non-magnetic grain boundary phase surrounding the plurality, the non-magnetic grain boundary phase being at least one of a group consisting of a metal oxide and a metal nitride, laminating a protective layer on the magnetic layer, laminating a liquid lubricant layer on the protective layer, and conducting the steps of laminating without a step of heating.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, further comprising the step of: forming a non-magnetic intermediate layer prior to the step of forming the magnetic layer, between the non-magnetic under-layer and the magnetic layer, the non-magnetic intermediate layer having a hexagonal close-packed structure.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, further comprising the step of: forming a non-magnetic alignment-control layer prior to forming the non-magnetic under-layer, and a preferential crystal orientation plane in a (100) plane parallel to a film surface of the non-magnetic alignment-control layer.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein the alignment-control layer includes at least one material selected from the group consisting of oxides of Mg, Ti, and V, and carbides and nitrides of Ti, Zr, Hf, Nb, Ta, Mo and W.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, further comprising the step of: forming a seed layer having amorphous structure between the non-magnetic alignment-control layer and the substrate.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: the seed layer includes a nickel layer containing from 10 at % to 40 at % of phosphorus.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: the seed layer includes a silicon layer containing from 25 at % to 55 at % of oxygen.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein the non-magnetic substrate includes at least a first substrate material selected from the group consisting of crystallized glass, chemically strengthened glass and resin.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: a step of heating the substrate is not performed preceding any one of the steps for lamination.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.